In recent years, high accuracy in retrieving target information from among information in an increasing information amount with development of networks is demanded.
When the amount of information is small, even when a retrieval result including noises (not intended result) is output, a user can find intended text by examining the retrieval result. However, when the amount of information is large, retrieval results increase, and it becomes difficult for a user to examine the retrieval results. Therefore, it is demanded that retrieval results with reduced noises be output.
One example of a retrieval method is explained referring to FIG. 18. FIG. 18 depicts one example of a retrieval method. As depicted in FIG. 18, a retrieval device that retrieves information performs, when text is input as search text, morphological analysis of the input text, to separate it in a word unit (S100). The retrieval device then compares separated words with a synonym dictionary in which synonyms are stored in advance (S110), generates a search word with a synonym including a matching word (S120). In the synonym dictionary, words regarded to have the same meaning in a word unit description are stored as synonyms. The retrieval device retrieves text that includes the search word from a search target document, as a retrieval result (S130, S140).
For example, in FIG. 18, suppose that a sentence “to display a clear image” is input as search text. The retrieval device then performs morphological analysis of the input sentence, to separate into words. As a result, the separated words are indicated as “image”, “clear”, “display”. The retrieval device compares the separated words with the synonym dictionary, and generates a search word with synonyms that include a matching word. Suppose that “clear, delete”, “display, express” are included in the synonym dictionary as synonyms. Accordingly, as search words, “image”; and “clear” or “delete”; and “display” or “expression” are generated. The retrieval device retrieves text that includes the search word from a search target document as a retrieval result. As a result, the retrieval device retrieves text of “to clear image data . . . ”, “delete a display of an old image . . . ”, and “clear a regular expression once . . . ” as the retrieval result (Japanese Laid-open Patent Publication No. 2015-60243).